A typical subsea wellhead assembly includes a wellhead housing that supports one or more casing hangers. One type of wellhead housing has a conical load shoulder machined within its bore. The casing hanger lands on and is supported by the load shoulder. In this type, the diameter of the housing bore below the bore is less than the diameter of the housing above the bore by a dimension equal to a radial width of the load shoulder.
In another type, referred to as “full bore”, the wellhead housing has a groove with substantially the same diameter above and below the groove. The load shoulder is a split ring that is installed subsequently in the groove. The casing hanger is supported by the load shoulder. This procedure allows a larger diameter bore to be employed during drilling operations. The load shoulder may be installed on a special running tool or it may be run with the casing hanger.